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A two fluid magneto-hydrodynamic theory of vacuum arc plasma jet propagation in a magnetized toroidal duct is developed. The physical mechanisms of jet transverse displacement and plasma losses are analyzed and the centrifugal force on the ions is shown to play the principle role in these processes. Optimal conditions for jet propagation occur when the centrifugal force is balanced by the electrical force on the ions. An analytical solution of the nonlinear problem of plasma beam transport through a toroidal duct is obtained for the two cases where ions are magnetized or not magnetized. The ion mass current decreases with the azimuthal distance along the torus as ͑1ϩ/ 0 ͒ Ϫ1 where 0 is a characteristic angular distance, for the case when ions are magnetized, and exponentially when the ions are not magnetized. Numerical calculations show that the decrease of plasma density leads to a longitudinal electric field and current. This current, together with the current due to the centrifugal drift, form a current loop which is closed through the plasma and structures outside the torus. Moreover if there are optimal conditions for jet propagation at the torus entrance, they are approximately conserved along the length of the torus.

Amorphous tin oxide films, 100-800 nm thick and of resistivity ∼6-8 m cm, were deposited on glass substrates using a filtered vacuum arc with an oxygen background gas pressure of 4.0 mTorr. The films were annealed in air at a temperature of 300˚C for 1, 3, 5, 7, and 10 min. Film morphology, structure, composition, roughness, and light transmission were determined before and after the annealing, on cold samples, with atomic force microscopy, x-ray diffraction diagnostics, x-ray photoelectron spectroscopy, and light transmission meter. The roughness depended weakly on the annealing time, and decreased with the thickness of the film. The film transmission in the visible region was practically independent of the annealing time. Film conductivity increased with the annealing time, reaching a maximum value after 3-7 min, larger by a factor of 2.0-2.9 than that measured before annealing. The oxygen to tin density ratio on the film surface decreased relative to its value before annealing and reached a minimum after annealing for 7 min. After annealing for 10 min, the O/Sn ratio increased relative to the minimum value but was lower than the ratio before annealing. The O/Sn ratio in the bulk decreased monotonically for annealing times longer than 1 min. The film conductivity before and after annealing depended linearly on the film thickness. A model is proposed to elucidate the dependence of the conductivity on the annealing time and on the film thickness.

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